The lint trap is the screen you pull out and clear after every load. The dryer vent is the duct that runs from the back of the machine to the outside of the house. A spotless trap says nothing about what is happening inside that duct, and treating the two as one part is where trouble starts in a lot of homes. Clearing the trap is a load-by-load habit. Clearing the vent is a different job entirely, one that reaches sections of duct a lint screen was never built to touch.
What the lint trap catches
The trap is built to catch the bulk of the lint a load sheds, the loose fibers that come off towels, sheets, and clothing as they tumble and dry. On a machine that gets cleared after every cycle, the screen does that job well for the lint it can reach. What it cannot reach is anything that slips past the mesh itself, around the frame where the screen seats into the housing, or through the short section of duct between the drum and the point where the trap sits.
What gets past a clean screen
No trap, cleared however often, catches everything that passes through it. Fine lint and the residue left behind by dryer sheets and fabric softener move past the mesh in small amounts on every load, and over months that adds up inside the duct behind the machine. That buildup is sticky rather than loose, which is why it clings to the inside of the vent instead of blowing straight through and out the exterior hood the way looser lint does.
Where that lint settles inside the vent
Lint that gets past the trap tends to collect at specific points rather than spreading evenly along the run. Bends and elbows slow the airflow enough for fibers to drop out of the airstream and stick there. The transition where flexible duct meets rigid duct is another common spot, along with any section where the diameter narrows or a screw was driven through the duct wall during installation, leaving a snag for lint to catch on. The exterior hood, where the duct meets the outside wall or roof, is the last stop, and it is often where a partial blockage becomes visible first.
What the exterior hood should tell you
With the dryer running, the hood on the outside of the house should show a steady flow of warm, humid air, and the flap or damper should swing open and stay open for the length of the cycle. A flap that barely moves, air that feels weak at the hood, or lint visibly caught in the flap itself all point to a restriction somewhere between the machine and the exterior, not to the trap, since the trap sits at the opposite end of that path.
Which part is on you, and which calls for a technician
Clearing the trap after every load is a homeowner job, and it is the single habit that keeps the bulk of lint from reaching the duct in the first place. The duct itself is a different kind of job. Clearing the full run calls for working in from both the machine connection and the exterior hood, since lint packed at a bend in the middle of a long run is not reachable from either end alone. Dryer Vent Cleaning covers that full path, not the first few feet nearest the machine. Where an inspection turns up a crushed section, a joint that has separated, or material that is too far gone to clean, Dryer Vent Installation replaces the damaged run instead of working around it.
Essex County rentals and two-family houses
This gap between the two parts shows up often in rentals and two-family houses across Essex County, where a tenant clears the trap every week without fail and the duct behind the wall goes years without anyone looking at it. The tenant assumes the vent is the landlord's concern since it is part of the building, and the landlord assumes the tenant is handling dryer upkeep since the laundry area sits inside the unit. Neither is wrong about their own piece, but the duct itself ends up belonging to no one in practice, and it is usually the stretch of run hidden inside a shared wall chase that goes longest without a look.
Lint that builds up along that hidden run is a recognized fire risk in clothes dryers, which is one reason the vent is worth checking on its own schedule rather than assuming a clean trap covers it.
A clean trap is good evidence that a habit is being kept, but it is evidence about the trap, not about the several feet of duct most homes have running out to the exterior. Treating the two as separate jobs, one by load and one on its own schedule, is what keeps both doing what they are supposed to do.